The present invention relates to a synergistic stabilizer combination useful for improving the resistance of polymers, such as olefin polymers and copolymers, to deterioration in physical properties due to heat, comprising a quinoline compound, a diamine compound and a magnesium compound, polymer compositions having an enhanced resistance to heat deterioration due to incorporation therein of such combinations, and to a process of preparing such polymer compositions.
Polymers, such as olefin polymers and copolymers, and particularly ethylene-vinyl acetate copolymers, have numerous valuable properties which permit them to be used in the manufacture of film, wire or cable coating, extruded profile shapes such as pipe, tubing, moldings etc. and extrusion coated paper, cloth, plastic films, etc. or various molded objects such as injection molded cups, containers, caps, toys, appliance parts, etc. and blow molded bottles, tanks, various shapes and the like. It has been observed, however, that such polymers under conditions of elevated temperature, particularly in the presence of atmospheric oxygen, undergo degradation, resulting in the deterioration of physical properties. Stabilization of such polymers is of utmost importance to industry in order to protect the polymer during fabrication and in use.
Considerable study has been devoted to the effects and prevention of thermal or heat degradation in polymers. Thermal degradation, as concerned with here, is usually oxidation occurring in ordinary atmospheres which varies or accelerates with increasing temperature and antioxidant materials have consequently been developed which provide a marked retardation of such thermal degradation. A thorough treatment of antioxidant materials and mechanisms can be found in the "Encyclopedia of Polymer Science and Technology", Volume 2, Interscience Publishers, pages 171-197. Amine antioxidants and combinations thereof are disclosed in the reference and on page 186, under section J, is disclosed a mixture of polymerized 1,2-dihydro-2,2,4-trimethyl quinoline and N,N'-diphenyl-p-phenylene diamine. U.S. Pat. Nos. 2,941,979; 2,955,100; 3,024,217; 3,367,903 and 3,657,203 are exemplary patents showing the use of antioxidants in polymer and rubber compositions. Unfortunately, these compounds and combinations thereof, have not provided the desired degree of protection of the polymer for many applications requiring enhanced protection from degradation at elevated temperatures.
One important application for a heat stabilized polymer is in electrical wire and cable coating applications. For these applications, it is important that the polymer wire sheathing have enhanced thermal stability especially when used as wiring for appliances. Appliances, such as electric ranges, clothes dryers, furnaces, irons, broilers, heaters and the like have a high thermal output and it is important that the insulated wire have thermal stability over a wide range of temperatures. For example, maintenance of physical properties of the polymer at an accelerated aged condition of seven days at 180.degree. C. is necessary for many such applications. A physical property of the polymer which is particularly important to be stabilized is the % Elongation. A marked decrease in this property over time at elevated temperatures significantly limits the polymers utility as wire sheathing since the polymer becomes brittle and cracks may develop during use.
It is an object of this invention to provide a new synergistic stabilizer combination for polymer compositions. Another object is to provide novel polymer compositions containing a synergistic combination of compounds that enhances the thermal stability of the polymer composition. Other objects of the invention will be apparent from the description and claims that follow.